http1: Remove redundant condition
http1: Remove redundant condition

`is_end_stream` must be always false in the else branch.

Fixes Coverity CID 1496186

yannick/h2o,cwyang/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,yannick/h2o,h2o/h2o,cwyang/h2o,h2o/h2o,h2o/h2o,h2o/h2o,devnexen/h2o,cwyang/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,cwyang/h2o,h2o/h2o,cwyang/h2o,yannick/h2o,cwyang/h2o,h2o/h2o,devnexen/h2o,cwyang/h2o,yannick/h2o,h2o/h2o,cwyang/h2o,devnexen/h2o